Not everything! Your just pointing out the bad link in the power chain!
The electrical utility companies have insurance policies just for when stuff like this happens. If they looked and said it was fine and you knew it wasn't they are liable for future damages because of incompetent workmanship or negligence.
Being you have tracked the voltage differential problem back to some point before your power box it is their responsibility. If its at the meter connection point or further up the supply line its still their responsibility.
As I recall the connections in the meter box are in fact the utility companies full responsibility not yours.
The actual connections you have responsibility for are the main lugs in the fuse or breaker box and forward.
I am not encouraging you to damage anything but unfortunately many professionals and service people dont do their jobs very well at all. Its only when they get their butts in trouble for sloppy work that they step up and do their own jobs right.
I dont see how they could consider a 10% voltage differential on the main lines a normal condition at that small of a load. It is not.
If I am remembering correctly I think the NEC code book calls for no greater than 5% line to line voltage differential when one half of a dual feed line system, standard 120/240 service, is loaded to its maximum main fuse or breaker rating.
That is if your main fuses are rated for 100 amps then if you had a 100 amp load pulling off of just one side of the service the voltage differential shall be no greater than 5% of the 120 volts from line to common. Or 114 volts on the load side and 126 volts on the unloaded side.
If your getting 109 and 136 volts on each side of the common with only 20 - 30 amps load you have a big problem and it has to be corrected.
And obviously you are trying to get that done.